Kbuild, link-vmlinux: Reuse vmlinux.o for final link
Even without kallsyms, link-vmlinux links the kernel twice: once
to generate a vmlinux.o for modpost and objtool, and another
time for the final executable.
This patch reuses the vmlinux.o to create the final executable
to avoid some redundant linking work.
Of course this particularly helps with Link Time Optimization, where
it prevents a double optimization of the whole kernel, but it's
midly beneficial on a standard build too.
This is a config option for now, but probably should be unconditional
at some point once all the architectures have been tested.
um support would need some extra work.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
diff --git a/init/Kconfig b/init/Kconfig
index 25c853e..9fc76c3 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1390,6 +1390,15 @@
arguments when it determines these arguments are very commonly
called. Experimential. Will increase text size.
+config SINGLE_LINK
+ bool "Use single linking step for final vmlinux"
+ default y if LTO
+ # for now. In theory should work everywhere except for um
+ depends on ARCH_SUPPORTS_LTO
+ help
+ Use only a single linking step for the final vmlinux, making
+ the build slightly faster.
+
config SYSCTL
bool
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index d4a786a..2bb8374 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -398,9 +398,23 @@
fi
fi
+if [ -z "${CONFIG_SINGLE_LINK}" ] ; then
+
info LDFINAL vmlinux
vmlinux_link vmlinux "${kallsymso} ${kallsymsorel}" ${btf_vmlinux_bin_o}
+else
+
+# Reuse the partial linking from the modpost vmlinux.o earlier
+
+info LD vmlinux
+${LD} ${KBUILD_LDFLAGS} ${LDFLAGS_vmlinux} \
+ -o vmlinux \
+ -T ${objtree}/${KBUILD_LDS} \
+ vmlinux.o ${kallsymso} ${kallsymsorel} ${btf_vmlinux_bin_o}
+
+fi
+
if [ -n "${CONFIG_KALLSYMS}" -a -n "${CONFIG_KALLSYMS_SINGLE}" ] ; then
# Now regenerate the kallsyms table and patch it into the
# previously linked file. We tell kallsyms to pad it
